Bayer MaterialScience One-Component And Two-Component Polyurethane Sealants – Composition, Advantages And Uses

Atlanta, GA - Although the terms “caulk” and “sealant” are often used interchangeably, they have fundamental differences. Caulks are used to fill a gap or crack and do not allow a lot of movement, while polyurethane sealants are more flexible and function as a barrier to water, air or other substances. Another difference is that sealants offer properties that are higher performing than caulking agents.

Polyurethane sealants are available in one-component (1K) or two-component (2K) formulations. Prepolymers in the backbone of the sealants provide most of the sealant’s properties.

Dr. Jay Johnston, senior scientist, Bayer MaterialScience LLC, provides a further explanation of sealants in his presentation “An Introduction to Silane Terminated Resins and Polyurethane Sealants,” at 10:50 a.m., Monday, April 22. Through his presentation, Dr. Johnston aims to educate attendees on polyurethane sealants – their composition, benefits and possible uses.

Traditional, moisture-cure 1K polyurethane sealants are usually based on aromatic diisocyanates. According to Dr. Johnston, benefits of this type of sealant include very little shrinkage, good flexibility, low modulus, excellent durability and paintability. Additionally, 1K polyurethane sealants are able to be formulated without the use of solvents. Possible foaming when in contact with large amounts of water and slow curing in low-humidity and cold conditions are some of the drawbacks of this technology.

A more recently developed 1K polyurethane sealant technology is based on silane-terminated prepolymers. The silane-terminated prepolymer eliminates the potential for the sealant to foam when in contact with moisture. This, along with colorfast properties, makes silane-terminated sealants attractive to the construction market.

1K polyurethane sealants are mainly used in fenestration applications, such as windows and doors, but can also be used in many other residential or construction applications. Dr. Johnston explains that since both variations of prepolymers are high-performing, moisture-cure 1K polyurethane sealants and 1K silane-terminated sealants continue to grow in popularity.

In his presentation, Dr. Johnston also details 2K polyurethane sealants. These formulations initially utilized polyurethane materials, but have now transitioned to using polyurea technology due to its faster reactivity. Polyureas also cure at low temperatures, making them well-suited for use in refrigeration or low-temperature, outdoor applications. Dr. Johnston adds that polyurea sealants also provide a quick return to service, are less moisture sensitive than 1K polyurethane sealants, prevent spalling of concrete into expansion joints and have good adhesion to most substrates, among other advantages.

“Applicators choose 2K sealants to create structural bonds in applications, such as in between concrete slabs, where strength is required,” says Dr. Johnston. “Unlike 1K polyurethane sealants, 2K sealants are not preferable for use around windows or doors. The 2K sealant formulas are too hard and strong – not providing the flexibility needed for those applications,” he concludes.